Ideally, golf club heads should be made with selective perimeter or heel, head, and toe weighting, adjustable densities, extended-life ball-striking surfaces, specific sonic characteristics, high friction surfaces, high ductility hosel and other desired mechanical properties, and an adjustable center of gravity.
At the present time such characteristics are achieved with varying degrees of success by the following: perimeter weighting and head and toe weighting are commonly used in forged and in investment cast clubs and desired weight distribution is achieved by shaping the club head to produce a cavity in the back of the club thus producing a complex shape known as cavity backed irons. In some cases, particularly putters, a cavity is provided in back of the club which is later filled with higher density metals by lead casting or gluing in place higher density metals. The resultant cavity is difficult to finish to a smooth surface by grinding and polishing and thus the club heads are not generally finished to a high polish. The raw, unfinished look of the cavity back is not attractive or well accepted by many skilled players but the improved performance provided by the cavity back and perimeter weighting is recognized as a benefit by players of all skill levels.
Adjustable densities in club heads are not possible using current forging and casting practices. The only method of changing density is to substitute one alloy for another, or by utilizing one or more weight ports where higher density disks or powders may be positioned and held in place by mechanically fastening or glue-bonding the enclosures in place. Additives of different density alloys to other primary alloys in the casting process will only produce a third alloy or a non- compatible mixture of metallic elements not suitable for use as golf club heads.
Extended-life ball-striking surfaces are presently produced by metal spraying a hard deposit on the surface of cast or forged clubs, and flame or case hardening the cast or forged clubs Additionally, ion implantation techniques may be used to harden a previously roughened surface. This is also accomplished by the teaching of U.S. Pat. No. 4,768,787, Shira, by producing a composite of hard particles in a softer metal matrix on the surface of the club. Extended life ball striking surfaces which are produced by hardening are temporary because of the thin surface developed by conventional techniques. The impact loading of the surface of golf clubs tends to peen and burnish the softer matrix material under the hard surface, thus destroying the desired roughness of the hardened surface material. Hard surfaces produced by flame spraying or plating a hard material on the surface of the golf club are often thin and quite brittle and tend to flake and peel under various service conditions.
Desired sonic characteristics are produced by selecting an alloy that, when properly heat treated, provides a sound when striking the ball that is deemed by experts to be desirable. The sound most desired is that of a ball striking a soft iron-carbon alloy commonly used for forged club heads. The hardness of this alloy is approximately Rockwell B85, a relatively soft, low-strength alloy. Clubs made of alloys with similar hardness levels are easily nicked and damaged by striking rocks and other hard objects, and wear rapidly by abrasion when used in sand traps and loam-type soils.
High friction surfaces are produced by sand blasting, flame spraying, and also by the use of hard particles in a softer metal matrix as is taught in U.S. Pat. No. 4,768,787, Shira.
At the present time, desirable properties in selected areas of a club head, such as a high ductility hosel, may be achieved by local heat treating using current technology but no manufacturers are known even to be using this technique.
Using present technology, the center of gravity of presently manufactured clubs is adjusted only by changing the shape, size and location of various portions of the club head or by utilizing suitably positioned weight ports holding appropriate dense materials.